Some Kentuckians have been finding an unwanted houseguest in recent weeks, the foreign grain beetle. This small beetle, also known as the new house beetle, makes unexpected appearances that can be hard to initially explain. They also resemble other insects, such as flour beetles and powderpost beetles, prompting concerns over stored products or the wood of a structure. Fortunately, there are ways to differentiate these diminutive beetles, and if it is the foreign grain beetle, there is usually no need to panic.
What is the foreign grain beetle?
This reddish-brown beetle, which measures under 1/8 inch long as an adult, is associated with areas of relatively high humidity (65% or more). They feed on fungal material that grows in these dampened areas, or they sometimes feed on stored or spilled grain. They can be identified by looking behind their head; the two front corners of the thorax will have distinct “pegs” that stick out.
They are most often confused for other insects like the sawtoothed grain beetle (which has a serrated-like edge to their thorax), the confused flour beetle (which is larger and has no thorax pegs), and occasionally for powderpost beetles (which also lack the pegs and do cause damage).
Figure 1: Starting from the left, a comparison of the foreign grain beetle, sawtoothed grain beetle, confused flour beetle, and a powderpost beetle. The foreign grain beetle is smaller than the others and if you look at the top two corners of its thorax, you will find small pegs the other species lack. (Photos: First three images by Ivy Orellana, University of Nebraska-Lincoln; powderpost beetle image by Pest and Diseases Image Library, Bugwood.org)
Why is it in my home?
This beetle is also known as the new house beetle because in houses that are 1 to 3 years old, they may emerge suddenly and in large numbers. The beetles were not hiding out and feeding on wood but took up residence on timber and in secluded areas while the house was being constructed. When wood is open and exposed to the elements, moisture can accumulate and lead to small growths of mold in the future. The beetles will feed on these pockets until there is nothing left, at which point they will disperse and be found around the home. They do fly towards lights and windows, where they may accumulate as they try to escape. This emergence tends to occur in late summer (around August or early September).
When found in older structures, they may be associated with a high humidity area of a home and serve as an indicator of a possible moisture issue. Their populations could occur in windowsills or behind wallpaper, anywhere that moisture may accumulate.
Is control necessary?
Usually, no action needs to be taken to deal with these insects.
- The food resources they are using are finite, and therefore, after 1 or maybe 2 or 3 cycles of this, the problem will dissipate.
- Increasing ventilation can help speed the process but would require construction help to increase the airflow.
- Sometimes, a moisture issue may need to be resolved in order cut off their food source, and then repair for any moisture damaged wood.
- Insecticide treatments, though, are unlikely to provide any relief from these pests without a high frequency of use. It is better to simply vacuum up beetles as they are discovered and know that they will soon be gone.
By Jonathan L. Larson, Entomology Extension Specialist
Kentucky Pest News 